This invention relates to N.sup.6,2'-O-dibutyryl-adenosine-3',5'-cyclic monophosphate monosodium sald (hereinafter abbreviated to DB.sub.c -AMP-N.sub.a) in a crystalline form, and in another aspect thereof to a process for producing DB.sub.c -AMP-N.sub.a in a crystalline form. According to the latter aspect of this invention, the process for producing DB.sub.c -AMP-N.sub.a in a crystalline form is characterized in that at least one kind of compound selected from an ether, a ketone, and an ester, as a crystallizing organic solvent, is caused to contact an alcoholic solution, aqueous alcoholic solution, or a simple aqueous solution of DB.sub.c -AMP-N.sub.a thereby to precipitate the DB.sub.c -AMP-N.sub.a out of the solution in a crystal form.
Alternatively, the process may comprise the steps of dissolving DB.sub.c -AMP-N.sub.a in a crude crystalline state or in an amorphous state in a mixture of the above-mentioned alcoholic liquid and the crystallizing organic solvent thereby to recrystallize the DB.sub.c -AMP-N.sub.a.
Adenosine-3',5'-cyclic monophosphate is naturally distributed widely in various biological worlds and has an important role in the vital phenomena thereof. DB.sub.c -AMP-N.sub.a, which is a useful derivative of the adenosine-3',5'-cyclic monophosphate, is recently attracting wide attention, and various fields of application therefor such as for medicine and biochemical reagents are now rapidly being developed
Heretofore, DB.sub.c -AMP-N.sub.a has been prepared as non-crystalline powder by freeze-drying, vacuum-drying, or some other method, out of its solution. However, since DB.sub.c -AMP-N.sub.a itself is extremely unstable, the purification thereof to a satisfactory degree is not practicable, and impurities (such as salts, coloring matters, or other minor ingredients) have been always contained in the resulting powdery product. Furthermore, the resultant DB.sub.c -AMP-N.sub.a in the form of non-crystalline powder is also unstable. This and the above described feature together with its extremely high hygroscopic property frequently constitute serious limitations in the production and the application of the product.